Light-triggered sustained release of pesticides

ABSTRACT

A process of forming a sustained-release pesticide coating, a process of forming a sustained-release pesticide capsule, and a sustained-release pesticide coating are disclosed. The process of forming the sustained-release pesticide coating includes depositing a first layer that includes a first pesticide onto a surface, and depositing a second layer that includes a photodegradable material onto the first layer. The process of forming the sustained-release pesticide coating also includes depositing a third layer that includes a second pesticide onto the second layer. The process of forming the sustained release pesticide capsule includes selecting a pesticide, selecting a photosensitive compound, and encapsulating the pesticide in a photosensitive capsule that includes a polymer formed from the photosensitive compound. The sustained-release pesticide coating includes a pesticide and a material having a photosensitive component. The material is in contact with the pesticide, and temporarily prevents the pesticide from contacting a surface.

BACKGROUND

The present disclosure relates to photodegradable materials and, morespecifically, to photodegradable materials for pesticide distribution.

Photodegradable materials are materials that decompose when exposed tolight. This decomposition can be reversible. Photodegradable materialsinclude materials made, at least in part, from photosensitive molecularcompounds (e.g., dimers, oligomers, and polymers that react withultraviolet (UV) light). Examples of photodegradable materials that canbe made from these compounds include plastics, fibers, paints, etc. Insome instances, photodegradable materials can offer protection from UVlight. For example, a material can be sprayed with a coating made thatincludes a photosensitive polymer. This polymer reacts with UV light,preventing the light from damaging the material under the coating. Othertypes of UV light protective materials can reflect UV light in order toprevent photodegradation of an underlying material.

SUMMARY

Various embodiments of the present disclosure are directed to a processof forming a pesticide coating. This process can include depositing afirst layer onto a surface, wherein the first layer includes a firstpesticide. The process can also include depositing a second layer ontothe first layer, wherein the second layer includes a photodegradablematerial, such as a coumarin-based hydrogel. Further, the process caninclude depositing a third layer onto the second layer, wherein thethird layer includes a second pesticide. The first pesticide and thesecond pesticide can be independently selected from a group consistingof a fungicide, an herbicide, an insecticide, a nematicide, amolluscicide, a piscicide, an avicide, a rodenticide, a bactericide,insect repellent, an animal repellent, and a disinfectant. Further, atleast one of the first layer and the second layer can include at leastone additional material, such as an additional pesticide, a binder, acarrier fluid, or an additive.

Additional embodiments of the present disclosure are directed to aprocess of forming a sustained-release pesticide capsule. This processcan include selecting a pesticide, selecting a photosensitive compound(e.g., a stilbenoid compound or a functionalized resveratrol dimer), andencapsulating the pesticide in a photosensitive capsule. Encapsulatingthe pesticide in the photosensitive capsule can involve forming a porousparticle, capping pores in the porous particle with a photosensitivepolymer formed from a stilbenoid compound, opening the pores by aphotochemical reaction, filling the open pores with the pesticide, andallowing the pores to close in the absence of actinic radiation.However, encapsulating the pesticide can alternately include adding anemulsifying agent to a mixture containing a functionalized resveratroldimer and the pesticide, adding a curing agent to the mixture, andforming a photodegradable shell around the pesticide in the absence ofactinic radiation. An additive (e.g., a colorant, a corrosion inhibitor,a stabilizer, a hardener, a co-solvent, and a plasticizer) can also beencapsulated in the photosensitive capsule. The process can also includeincorporating the capsule into a polymer matrix.

Further embodiments of the present disclosure are directed to asustained-release pesticide coating. The coating can include at leastone pesticide and a material in contact with the at least one pesticide.The material can include a photosensitive component. Additionally, thematerial can temporarily prevent contact between the at least onepesticide and a surface. The material can be a coumarin-based hydrogel,a photodegradable capsule, or a capsule having pores capped by aphotosensitive polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a process of preparing asustained-release pesticide coating, according to some embodiments ofthe present disclosure.

FIG. 2A is a chemical structure diagram illustrating molecularstructures of sustained-release pesticide coating components, accordingto some embodiments of the present disclosure.

FIG. 2B is a chemical structure diagram illustrating a photodegradablecoumarin-based hydrogel, according to some embodiments of the presentdisclosure.

FIG. 3 is a flow diagram illustrating a process of preparingsustained-release pesticide capsules, according to some embodiments ofthe present disclosure.

FIG. 4A is a chemical reaction diagram illustrating a process of formingphotodegradable sustained-release pesticide capsules, according to someembodiments of the present disclosure.

FIG. 4B is a chemical reaction diagram illustrating processes of formingand decomposing photodegradable capsules, according to some embodimentsof the present disclosure.

FIG. 5 is a chemical reaction diagram illustrating a process of formingporous sustained-release pesticide capsules, according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

Current agricultural techniques rely on pesticides to protect crops thatprovide food for human and animal consumption, as well as raw materialsfor applications such as textiles, lumber, and pharmaceuticals. Apesticide is any substance or mixture of substances intended to protectagainst pests (e.g., organisms that may interfere with crop growth). Theterm pesticide can refer to fungicides, herbicides, insecticides,nematicides, molluscicides, piscicides, avicides, rodenticides,bactericides, insect repellents, animal repellents, disinfectants, orcombinations thereof. A wide array of pesticides has been developed inorder to provide varying levels of cost, resistance to environmentalfactors (e.g., rain, sun, wind, air pollution, etc.), safety, targetedorganism specificity, etc.

The pesticide chosen for a given application depends on a variety offactors. For example, the role of a pesticide in the protection of aselected plant is considered. Pesticides can offer preventativeactivity, early-infection activity, pest eradication, and/oranti-sporulant activity. The pesticide's mobility within a plant canalso be considered. For example, contact pesticides remain on thesurface of a plant, while systemic pesticides are absorbed into theplant tissue. Further, pesticides can be selected based on their mode ofaction and breadth of activity. The mode of action refers to how apesticide acts on a target organism (e.g., by damaging cell membranes,inactivating specific enzymes, or interfering with metabolic processes),and the breadth of activity refers to the number of sites on which thepesticide acts. For example, some pesticides act against a single stepin an organism's metabolic processes, while other pesticides act againstmore than one step in at least one metabolic process. Otherconsiderations take the class of chemical compound of the pesticide intoaccount. For example, a particular fungicide may not be chosen to actagainst a fungus when the fungicide is in a class of compounds that aretoxic to a local crop or animal population.

It is advantageous to avoid depositing more pesticide than is necessary.Excess pesticides may harm the protected crop, as well as otherorganisms that are not the intended target. Further, over-application ofpesticides is costly, wasteful, and time-consuming. However, asignificant quantity of applied pesticides is lost or destroyed beforethe pesticides can be effective. For example, pesticides on a plantsurface can be washed away by rain. Therefore, excess pesticides areoften necessary in order to counteract this loss. In some instances,pesticide coatings are applied at regular intervals in order to replacethose that are washed away, reacted with an organism, or absorbed byplants and soil. This requires a great deal of time, labor, andmaterials.

Processes and materials for sustained release of pesticides aredisclosed herein. Sustained release of pesticides reduces the number ofapplications and overall quantity of pesticide needed because thepesticides are protected from the environment prior to release.Additionally, a free pesticide can be applied with a protect pesticide,and can act against the organism before the next pesticide is released.The pesticides are gradually released as a protective photosensitivematerial (e.g., a polymeric coating or capsule) reacts with actinicradiation. Actinic radiation is electromagnetic radiation capable ofproducing a photochemical reaction. Actinic radiation (e.g., UV light)can be provided by sunlight. However, artificial light is used in otherembodiments, either in combination with sunlight or alone. For example,indoor farming or gardening techniques (e.g., hydroponics, aeroponics,and aquaponics) use artificial light (e.g., incandescent lamps,fluorescent lamps, or light-emitting diodes) to provide actinicradiation.

FIG. 1 is a flow diagram illustrating a process 100 of preparing asustained-release pesticide coating, according to some embodiments ofthe present disclosure. In this example, the sustained-release pesticidecoating is deposited onto the surface of crops or other plants. However,it should be noted that the sustained-release pesticide coating can beapplied to other surfaces (e.g., surfaces of outdoor furniture, campingequipment, boating equipment, etc.) in some embodiments.

In process 100, a first layer of pesticide is applied to a plantsurface. This is illustrated at step 110. The first layer of pesticideis referred to herein as the pesticide underlayer. Examples oftechniques that can be used to apply the pesticide underlayer includespraying, dipping, curtain casting, and/or cascade casting. Thisunderlayer includes at least one variety of pesticide. In someembodiments, the pesticide underlayer is directed to a single type oforganism (e.g., a fungus). In other embodiments, the pesticideunderlayer includes a combination of pesticides directed to more thanone type of organism. The pesticide underlayer may also includematerials (e.g., binders, additives, and carrier fluids) other than theselected pesticide or pesticides. This is discussed in greater detailbelow.

Examples of pesticides that can be used can include fungicides (e.g.,azoxystrobin, azadirachtin, captan, chlorothalonil, copper sulfate,etridiazole, fenarimol, flutolanil, fosetyl-aluminum, iprodione,mancozeb, maneb, metalaxyl, myclobutanil, pentachloronitrobenzene(PCNB), propamocarb, propiconazole, streptomycin sulfate, sulfur,thiabendazole, thiophanate-methyl, triadimefon, triforine, vinclozolin,and/or ziram), insecticides (e.g., acephate, bendiocarb, bifenthrin,carbaryl, chlorpyrifos, cyfluthrin, cypermethrin, diazinon, dimethoate,esfenvalerate, fenbutatin oxide, hexythiazox, imidachloprid,lambda-cyhalothrin, malathion, permethrin, petroleum distillates,potassium salts of fatty acids, pymetrozine, pyrethrins, rotenone,spinosad, and trichlorfon), and herbicides (e.g.,2,4-dichlorophenoxyacetic acid, arsenic acid, benefin, bensulide,bentazon, clopyralid, corn gluten meal, dicamba salt, diquat dibromidesalt, dithiopyr, S-ethyl-N,N-dipropylthiocarbamat (EPTC),fluazifop-p-butyl, glufosinate isopropylamine salt, halosulfuron,isoxaben, mecoprop, metolachlor, monosodium methanearsonate (MSMA),napropamide, oryzalin, oxadiazon, pelargonic acid, pendimethalin,prodiamine, siduron, simazine, triclopyramine, and/or trifluralin).However, any appropriate pesticide may be used, such as nematicides,molluscicides, piscicides, avicides, rodenticides, bactericides, insectrepellents, animal repellents, or disinfectants.

A binder is added to the pesticide underlayer in some embodiments.Binders are polymer adhesives that aid in forming a pesticide coating ona surface. Examples of compounds that can be used as binders can includealginates, cellulose-based polymers (e.g., carboxymethylcellulose,cellulose acetate phthalate, hydroxymethyl cellulose, methyl cellulose,etc.), gelatin, natural gums (e.g., gum arabic, locust bean gum,carrageenan gum, xanthan gum, etc.), pectins, starch-based polymers(e.g., carboxymethylstarch), poly(acrylates) (e.g., poly(acrylic acid)and poly(methacrylic acid)), poly(ethers), poly(acrylamides), poly(vinylalcohol), maleic anhydride copolymers, hydrolyzed acrylonitrile graftedstarch, acrylic acid grafted starch, poly(N-vinyl pyrrolidine),poly(2-hydroxyethylacrylate), poly(2-hydroxyethyl-methacrylate),poly(sodium acrylate-co-acrylic acid), poly(vinyl sulfonates),poly(vinylsulfonic acid), poly(ethylene oxide), block copolymers ofethylene oxide with polyamides, polyesters, or polyurethanes, and saltforms, mixtures, and/or copolymers thereof.

Further, the pesticide underlayer can include a carrier fluid. A carrierfluid is a liquid, such as an organic solvent or water, that allowscoatings to flow and be applied via various methods (e.g., spraying,dipping, curtain casting, and/or cascade casting). A carrier fluid canbe added to the pesticide underlayer in order to facilitate itsapplication. Examples of organic solvents that may be used as carrierfluids include acetic acid, acetonitrile, acetone, butyl alcohol,dichloromethane, dimethylformamide, dimethylsulfoxide, 1,4-dioxane,ethanol, formic acid, isopropanol, methanol, n-propanol,tetrahydrofuran, and mixtures and/or aqueous solutions thereof. However,in some embodiments, the pesticide underlayer is applied to a surfacewithout a carrier fluid.

Additives can optionally be included in the pesticide underlayer aswell. Additives are compounds that contribute additional functionalityto a material. Additives can be included in the pesticide underlayer inorder to provide functions other than biocide activity, adhesion, orapplication facilitation. For example, colorants (e.g., pigments and/orfluorescent dyes) can be added. Colorants aid in indicating the extentof crop coverage. Other additives that may be used can include corrosioninhibitors, stabilizers, hardeners, co-solvents for increasingviscosity, and plasticizers for increasing the uniformity of thecoating.

After application of the pesticide underlayer at step 110, aphotodegradable material is deposited onto the pesticide underlayer.This is illustrated at step 120. The photodegradable material can bedeposited by spraying it onto the pesticide underlayer in someembodiments. However, any appropriate application method can be used(e.g., dipping, curtain casting, or cascade casting). Thephotodegradable material is a coumarin-based hydrogel that decomposeswhen exposed to actinic radiation. A hydrogel is a cross-linked polymernetwork that retains a significant fraction of water within itsstructure, but does not dissolve in water. The structure and synthesisof coumarin-based hydrogels are discussed in greater detail with respectto FIGS. 2A and 2B. The coumarin-based hydrogels illustrated hereindecompose when exposed to electromagnetic radiation having wavelengthsranging from approximately 250 nm-450 nm. However, electromagneticradiation at other wavelengths (e.g., approximately 100 nm-500 nm) canalso cause decomposition of these photodegradable materials.

Another layer of pesticide is then deposited onto the photodegradablelayer. This is illustrated at step 130. This layer of pesticide isreferred to herein as the pesticide overlayer. The pesticide overlayerincludes at least one variety of pesticide. In some embodiments, thepesticide overlayer has the same composition as the pesticideunderlayer. However, in other embodiments, the overlayer may include adifferent combination of pesticides, binders, additives, and/or carrierfluids than that of the underlayer. Examples of pesticides, binders,additives, and carrier fluids that can be included in the pesticideoverlayer are discussed in greater detail with respect to the pesticideunderlayer. The three layers applied in process 100 provide a sustainedrelease pesticide coating. The pesticide underlayer immediately actsagainst targeted organisms (e.g., fungi, viruses, or bacteria) on thesurface or interior of the plant. Then, as the photodegradable materialdecomposes, the plant surface is exposed to the pesticide overlayer.

FIG. 2A is a chemical structure diagram 200 illustrating molecularstructures of sustained-release pesticide coating components, accordingto some embodiments of the present disclosure. The illustrated pesticidecoating components are units in a photodegradable coumarin-basedhydrogel. The coumarin-based hydrogel units include 4-armed polyethyleneglycol (PEG) compounds. An example 4-armed PEG compound 210 isrepresented by a generic structure that has R functional groups. The Rgroups on the 4-armed PEG compound 210 are either alkyne-terminated Rgroups 230 or coumarin azide-terminated R groups 240.

In an example synthesis (not shown) of a 4-armed PEG compound 210 withalkyne-terminated R groups 230, excess triethylamine is added to adichloromethane (DCM) solution of a 4-armed PEG amine-HCl. A 4-armed PEGamine-HCl of any average molecular weight (e.g., in a range ofapproximately 300 Da-20,000 Da) can be selected. The molecular weight ofeach ethylene glycol repeat unit —OCH₂CH₂— is 44.05 Da. The DCM solutionis stirred at room temperature (e.g., approximately 25° C.-30° C.).After the DCM solution has stirred at room temperature for approximately15 minutes, excess 4-pentynoic acid, diisopropyl carbodiimide, anddimethyl aminopyridine are added to the solution at ice bath temperature(e.g., approximately 10° C.-15° C.). This mixture is then warmed to roomtemperature, and stirred for approximately twenty-four hours. After thisperiod of stirring, the mixture is added dropwise to cold diethyl ether.The resulting precipitate is centrifuged, and the supernatant fluid isdecanted. The precipitate is allowed to dry, and then dissolved indistilled water. This solution is dialyzed against a large volume ofwater (e.g., approximately two liters) for approximately twenty-fourhours. The dialyzed solution is then lyophilized to obtain the 4-armedPEG compound 210 with alkyne-terminated R groups 230.

In an example synthesis (not shown) of a 4-armed PEG compound 210 withcoumarin azide-terminated R groups 240, excess N,N-diisopropylethylamine (DIEA, Hunig's base) is added to a dichloromethane (DCM)solution of a 4-armed PEG tetra-carboxylic acid, followed by1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium3-oxidhexafluorophosphate (HATU). A 4-armed PEG tetracarboxylic acid ofany appropriate average molecular weight (e.g., in a range ofapproximately 300 Da-20,000 Da) can be selected. A DCM solution ofcoumarin azide and DIEA are next added to the solution at ice bathtemperature (e.g., approximately 10° C.-15° C.). The mixture warmed toroom temperature, and stirred for approximately twenty-four hours beforebeing added dropwise to cold diethyl ether. The resulting precipitate iscentrifuged, and the supernatant fluid is decanted. The precipitate isallowed to dry, and then dissolved in distilled water. This solution isdialyzed against a large volume of water (e.g., approximately twoliters) for approximately twenty-four hours. The dialyzed solution isthen lyophilized to obtain the 4-armed PEG compound 210 with coumarinazide-terminated R groups 240.

FIG. 2B is a chemical structure diagram illustrating a photodegradablecoumarin-based hydrogel 245, according to some embodiments of thepresent disclosure. This hydrogel 245 is an example of a hydrogel thatcan be applied as a photodegradable layer at step 130 of process 100,which is illustrated in FIG. 1. The coumarin-based hydrogel 245 can beformed in a copper(I)-catalyzed azide-alkyne cycloaddition reactionbetween the 4-armed PEG compound 210 with coumarin azide-terminated Rgroups 240 and the 4-armed PEG compound 210 with alkyne-terminated Rgroups 230. However, in some embodiments, the hydrogel 245 is formed ina strain-promoted azide-alkyne cycloaddition reaction between theaforementioned types of 4-armed compound 210. The hydrogel 245 hasalternating PEG units 250 (dotted lines) and 260 (bold lines) providedby the 4-armed PEG compounds 210, which are linked by photodegradablecoumarin units 270 (gray ovals). The dashed lines at the edges of thehydrogel 245 structure represent additional PEG units outside of theportion of the hydrogel 245 illustrated in FIG. 2B. It should be notedthat, although FIG. 2B illustrates a two-dimensional (2D) portion of thehydrogel, coumarin-based hydrogels are three-dimensional (3D).

FIG. 3 is a flow diagram illustrating a process 300 of preparingsustained-release pesticide capsules, according to some embodiments ofthe present disclosure. This type of capsule includes a photodegradablecapsule material that encloses a pesticide payload. Capsules of anyappropriate size can be formed (e.g. approximately 10 nm-1000 μm indiameter). For example, the capsules can be microcapsules ranging fromapproximately 10 μm-1000 μm in diameter. In some embodiments, thecapsules are nanocapsules ranging from approximately 10 nm-1000 nm indiameter. Herein, “capsule” can refer to either a microcapsule or ananocapsule, unless otherwise specified.

Process 300 begins with the selection of a pesticide for the capsulepayload. This is illustrated at step 310. Examples of pesticides thatcan be selected include fungicides, insecticides, and herbicides.Examples of fungicides, insecticides, and herbicides that can be usedare discussed in greater detail with respect to FIG. 1. It is noted thatother pesticides can be used in some embodiments, such as nematicides,molluscicides, piscicides, avicides, rodenticides, bactericides, insectrepellents, animal repellents, disinfectants. Additionally, the payloadcan include more than one type of pesticide. Additives can be includedin the payload as well (e.g., stabilizers, solvents, viscositymodifiers, odorants, colorants, blowing agents, antioxidants, curingagents, etc.).

A photosensitive compound is then selected. This is illustrated at step320. In some embodiments, the photosensitive compound is a resveratroldimer that undergoes retro-dimerization when exposed to actinicradiation. The resveratrol dimer can be functionalized, and reacts toform a photodegradable polymeric shell. This is discussed in greaterdetail with respect to FIGS. 4A and 4B. In other embodiments, thephotosensitive compound a stilbenoid compound, which forms aphotosensitive polymer. This is discussed in greater detail with respectto FIG. 5. It should be noted that the selection of the pesticide atstep 310 is illustrated as occurring after the selection of thephoto-cleavable polymer at step 320. However, in some embodiments, step310 can occur before step 320. Further, steps 310 and 320 can occursimultaneously in some embodiments.

The selected pesticide and photosensitive compound are used to formsustained-release pesticide capsules. This is illustrated at step 330.The photosensitive compounds are used in the encapsulation of thepesticide and any other payload components. For example, the pesticidecan be contained inside of a photodegradable capsule, or inside ofcapped pores in a porous capsule. When the capsules are exposed toactinic radiation, the pesticide and other payload components arereleased. The release occurs because of a photochemical reaction thatleads to either capsule shell decomposition or pore opening. The type ofrelease depends upon the type of capsule (e.g., a photodegradablecapsule or a porous capsule). The capsules are deposited as pesticidecoatings. In some embodiments, these coatings include additionalmaterials (e.g., polymer matrices, carrier fluids, and/or additives).Techniques for applying pesticide coatings can include spraying,dipping, curtain casting, and/or cascade casting.

In some embodiments, the capsules have orthogonal functionalitiesprovided by surface functional groups. This functionality can beprovided by functional groups on compounds used to form the capsules, orby functional groups added by surface modification of the capsules.Orthogonal functionalities can facilitate incorporation of capsules intoa polymer matrix by enabling binding of the polymer to the capsulesurface. Further, orthogonal functionalities can enable binding ofadditives to the capsules. However, it should be noted that, in someembodiments, the capsules have no surface functional groups that can actas orthogonal functionalities. Capsules without surface functionalgroups, or with surface-bound additives, can be incorporated intopolymer matrices by blending.

Examples of polymer matrices into which the capsules can be incorporatedcan include alginates, cellulose-based polymers (e.g.,carboxymethylcellulose, cellulose acetate phthalate, hydroxymethylcellulose, methyl cellulose, etc.), gelatin, natural gums (e.g., gumarabic, locust bean gum, carrageenan gum, xanthan gum, etc.), pectins,starch-based polymers (e.g., carboxymethylstarch), poly(acrylates)(e.g., poly(acrylic acid) and poly(methacrylic acid)), poly(ethers),poly(acrylamides), poly(vinyl alcohol), maleic anhydride copolymers,hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch,poly(N-vinyl pyrrolidine), poly(2-hydroxyethylacrylate),poly(2-hydroxyethyl-methacrylate), poly(sodium acrylate-co-acrylicacid), poly(vinyl sulfonates), poly(vinylsulfonic acid), poly(ethyleneoxide), block copolymers of ethylene oxide with polyamides, polyesters,polyurethanes, and salt forms, mixtures, and/or copolymers thereof.

As discussed above, additives can be bound to orthogonal functionalitieson the capsules. However, additives can also be incorporated intopolymer matrices containing the capsules, and/or mixed with carrierfluids containing the capsules. These additives may include colorants,corrosion inhibitors, stabilizers, hardeners, viscosity modifiers,plasticizers, etc. Additionally, the sustained-release pesticidecapsules can be combined with an un-encapsulated pesticide (e.g., in thepolymer matrix or carrier fluid). The pesticide that is not encapsulatedimmediately acts against a targeted organism. Then, when the capsulesare exposed to actinic radiation, the plant surface is gradually exposedto the released pesticide payload.

FIG. 4A is a chemical reaction diagram illustrating a process 400 offorming photodegradable sustained-release pesticide capsules, accordingto some embodiments of the present disclosure. These photodegradablecapsules provide a first example of pesticide capsules that can be usedin process 300, which is illustrated in FIG. 3. The illustratedphotodegradable capsule 405 includes a payload droplet 410 containingpesticide surrounded by a photodegradable shell 415. The shell 415 isillustrated as having orthogonal functionalities, which are representedby stars. The orthogonal functionalities can bind to additives (e.g.,additional pesticides) and/or a polymer matrix. However, in someembodiments the shell 415 is not functionalized. Though FIG. 4Aillustrates a cross-sectional view of the photodegradable shell 415, itshould be understood that the shell 415 completely encapsulates thepayload 410.

In process 400, the functionalized resveratrol dimers 420 are added to astirring aqueous solution containing an ethylene maleic anhydride (EMA)surfactant, urea, and ammonium chloride (NH₄Cl). The functionalizedresveratrol dimers 420 are illustrated as gray curved lines having starsat each end, which represent functional groups (e.g., allyl, vinyl,meth(acrylate), or epoxy groups) that will provide orthogonalfunctionality to the photodegradable capsule 405. However, it should benoted that, in other embodiments, the dimers 420 may each have only oneof these functional groups, or may have none. In these instances, aphotodegradable capsule without orthogonal functionalities can beformed. The pH of the aqueous solution containing the functionalizedresveratrol dimers 420 is adjusted to approximately 3.5 by adding acidand base (e.g., hydrochloric acid (HCl) and sodium hydroxide (NaOH)).The payload 410 is dispersed in the aqueous phase. The payload 410includes at least one type of pesticide. Further, the payload 410 canoptionally include additional payload components. Examples of payloadcomponents that may be included are discussed in greater detail withrespect to FIG. 3.

An emulsifying agent 425 is added to the mixture as it continuesstirring. The emulsifying agent 425 is an appropriate oil-in-wateremulsifier (e.g. an emulsifier selected from emulsifiers havinghydrophilic-lipophilic balance (HLB) values greater than 8). Examples ofemulsifiers such as these include polysorbate 60, polysorbate 80,sorbitan laurate, cetearyl glucoside, oleth-10, oleth-20, PEG-7 olivate,PEG-8 oleate, PEG-8 laurate, PEG-20 almond glycerides, PEG-60 almondglycerides, etc. In FIG. 4A, molecules of the emulsifying agent 425 arerepresented by black wavy lines, which each have a gray sphere at oneend. The black wavy lines represent the hydrophobic regions of themolecules of emulsifying agent 425, and the gray spheres represent thehydrophilic regions.

A curing agent is added to the mixture in order to complete the reactionbetween the functionalized resveratrol dimers 420 and the emulsifyingagent 425. In some embodiments, the curing agent is formaldehyde.However, other curing agents can be used, such as triazone resins orphenol formaldehyde resins. This reaction causes the shell 415 to formaround a droplet of payload 410. Formation of the shell 415 occurs inthe absence of actinic radiation (e.g., when the reaction mixture isexposed to electromagnetic radiation at wavelengths above approximately300 nm). This is discussed in greater detail with respect to FIG. 4B. Itshould be noted that, for simplicity, FIG. 4A illustrates a small numberof molecules 420 and 425, which are not to scale with the payloaddroplet 410. However, process 400 includes a sufficient quantity ofresveratrol dimers 420 and emulsifying agent 425 to form shells around,at least, the majority of payload droplets in the mixture.

In some embodiments, the photodegradable capsules formed in process 400are microcapsules (e.g., approximately 10 μm-1000 μm in diameter).However, other sizes can be formed as well. The average size of thecapsules depends, at least in part, upon the stir speed during theemulsification and capsule formation. For example, finer capsules (e.g.,approximately 10 nm-10 μm in diameter) can be formed at higher stirspeeds. The size of the capsules also be influenced by other factors,such as temperature and/or reaction components. The capsules areoptionally combined with polymer matrices, carrier fluids, and/oradditives, and are then deposited onto surfaces as pesticide coatings.This is discussed in greater detail above.

FIG. 4B is a chemical reaction diagram illustrating processes 430, 450,and 460 of forming and decomposing photodegradable capsules, accordingto some embodiments of the present disclosure. An example of aphotodegradable capsule 405 such as these is illustrated in FIG. 4A. Inprocess 430, a resveratrol derivative 435 is dissolved in water (H₂O),ethanol (EtOH), or an H₂O/EtOH mixture. The resveratrol derivative 435can be obtained from commercial sources, or it can be synthesized (e.g.,by reacting resveratrol with an allyl source, such as an allyl halide,in the presence of triethylamine and tetrahydrofuran at approximately 0°C.). The resveratrol derivative 435 in process 430 has an allylfunctional group. However, resveratrol derivatives with other functionalgroups (e.g., vinyl, meth(acrylate), or epoxy) can be used. Further, theresveratrol derivative 435 can be replaced with non-functionalizedresveratrol (3,5,4′-trihydroxy-trans-stilbene) in some embodiments.

The resveratrol derivatives 435 dimerize in the absence of actinicradiation. To accomplish this reaction, the resveratrol derivative 435solution is exposed to electromagnetic radiation at wavelengths greaterthan approximately 300 nm (e.g., approximately 290 nm-800 nm). Forexample, light in the visible (390 nm-700 nm), UV-A (320 nm-400 nm),and/or UV-B (290 nm-320 nm) ranges can be used. Radiation at lowerwavelengths (e.g., approximately 240 nm or below) can causeretro-dimerization of the dimer 445, thereby inhibiting the reaction. Inthe absence of actinic radiation (e.g., approximately 100 nm-240 nm)molecules of the resveratrol derivative 435 form an allyl-functionalizedresveratrol dimer 445 (referred to herein as an allyl resveratrol dimer445). The allyl resveratrol dimer 445 is a photosensitive compound thatcan form a photodegradable polymer.

In process 450, a photodegradable shell is formed from the allylresveratrol dimers 445. This includes polymerization of the allylresveratrol dimers 445. The polymerization occurs in an emulsificationprocess for forming a sustained-released pesticide capsule. This isdiscussed in greater detail with respect to FIG. 4A. The resultingcapsule shell polymer includes a network of connected photosensitivedimer units 455, each provided by an allyl resveratrol dimer molecule445. The shell can also include other units and/or bound molecules(e.g., resveratrol monomer units, alternate resveratrol-derived dimerunits, cross-linkers, additives, etc.). The locations of bondsconnecting the photosensitive dimer units 455 of the shell polymer arerepresented by wavy dotted lines. In this example, the photosensitivedimer units 455 also have orthogonal functionalities provided by theallyl functional groups of the allyl resveratrol dimers 445. The allylfunctional groups can bind to a polymer matrix, additive, and/orpesticide. These binding locations are represented by wavy solid lines.It should be noted that, in some embodiments, there are no orthogonalfunctionalities (e.g., when the allyl resveratrol dimers 445 arereplaced by non-functionalized resveratrol dimers).

In process 460, the photosensitive dimer units 455 of the shell polymerare photochemically cleaved in a retro-dimerization reaction.Retro-dimerization occurs when the dimer units 455 are exposed toelectromagnetic radiation (e.g., at wavelengths of approximately 240 nmor lower). The retro-dimerization reaction may also be promoted byradiation at wavelengths of up to approximately 290 nm. For example,photodegradable capsules that include the photosensitive units 455 canbe exposed to UV-C radiation (100 nm-290 nm). Simultaneous exposure ofthe photosensitive units 455 to radiation at higher wavelengths (e.g.,approximately 250 nm-800 nm) does not prevent the retro-dimerizationfrom occurring. When a capsule having a shell formed from resveratroldimers is exposed to actinic radiation, photocleavage of thephotosensitive units 455 produces a photodegraded polymer that includesresveratrol monomer units 465. Actinic radiation is provided by sunlightor artificial light (e.g., incandescent lamps, fluorescent lamps, orlight-emitting diodes). This photodegradation of the polymer allowspesticides to be released from the capsule.

FIG. 5 is a chemical reaction diagram illustrating a process 500 offorming porous sustained-release pesticide capsules 505, according tosome embodiments of the present disclosure. These porous capsules 505provide a second example of pesticide capsules that can be used inprocess 300, which is illustrated in FIG. 3. Each capsule 505 includespores containing a pesticide, which are capped by a photosensitivepolymer that prevents the pesticide from being released. However, due tothe photosensitivity of the capping polymer, the pores are able to openand close in response to electromagnetic radiation at appropriatewavelengths.

Examples of a porous sustained-release pesticide capsule 505, a cappedparticle 510, and an uncapped particle 520 are illustrated as light grayspheres with dots representing pores. Capped pores are represented bydark gray dots, and uncapped pores are represented by black dots. Thisis intended to provide a simplified illustration, and it should beunderstood that the dots and spheres are not to scale, and are notintended to represent the actual appearance or structure of the capsules505 or particles 510 and 520. In some embodiments, the poroussustained-release capsules 505 are nanocapsules having an average sizeof approximately 200 nm in diameter, and an average pore size ofapproximately 2-3 nm in diameter. However, capsules 505 of other sizes(e.g., ranging from approximately 10 nm-1000 μm in diameter) can beformed under appropriate reaction conditions, as would be understood bya person of ordinary skill in the art.

Process 500 begins with the provision of particles 510 having pores thatare capped with a photosensitive polymer. The capped particles 510 canbe synthesized in situ, or obtained from another source (e.g., acommercial entity or a research institution). In an example of a process(not shown) of forming the capped particles 510, porous silicananoparticles are first prepared by dissolving approximately 3×10⁻³ moln-cetyltrimethylammonium bromide (CTAB) in water (e.g., 500 mL water).Approximately 3-4 mL of an aqueous solution of sodium hydroxide (e.g.,approximately 2 M NaOH_((aq))) is then added to the solution, and thetemperature is adjusted to approximately 80° C. Approximately 3×10⁻² moltetraethyl orthosilicate (TEOS) is added dropwise to the solution,followed by dropwise addition of approximately 5×10⁻³ mol3-mercaptopropyltrimethoxysilane (MPTMS). This mixture is then stirredfor approximately two hours. The solid product of this reaction isfiltered, washed with methanol and deionized water, and dried.

The resulting dried porous silica nanoparticles have surfactant (CTAB)remaining in their pores. Without removing the surfactant, the poroussilica nanoparticles are mixed with a vinylsilane, and refluxed forapproximately twenty-four hours in ethanol. During this period ofrefluxing, vinyl-modified porous silica nanoparticles are formed. Theseparticles are washed with ethanol and methanol in order to removeremaining surfactant. The particles are then dried (e.g., at 80° C. invacuo) in order to remove remaining solvent from their pores. Afterdrying, the vinyl-modified porous silica nanoparticles are reacted in across-metathesis reaction with a photosensitive dimerizable stilbenoidcompound 540. Though the stilbenoid compound 540 is illustrated as being(E)-1,3-bis(allyloxy)-5-(4-(allyloxy)styryl)benzene, other compoundsthat are capable of dimerization and retro-dimerization reactions whenexposed to actinic radiation are used in some embodiments. Examples ofphotosensitive dimerizable compounds that may be used can includeanthracenes, phenanthrenes, coumarin derivatives, hydroxycinnamatederivatives, alternate stilbenoids, etc. The dimerizable compound 540forms a polymer in the cross-metathesis reaction. This polymer caps thesilica nanoparticle pores, thereby producing the capped particles 510.

Process 500 continues with the reversible opening of the pores in thecapped particles 510. The capped particles 510 are exposed to actinicradiation (e.g., electromagnetic radiation at wavelengths ofapproximately 240 nm or lower) while suspended in water, an organicsolvent, and/or a polymer matrix. When the capped particles 510 areexposed to the actinic radiation, retro-dimerization of units in thephotosensitive polymer occurs. This opens the pores by breaking bonds inthe capping photosensitive polymer, yielding the uncapped particle 520.The capped particles 510 are mixed with payload components before,during, and/or after this exposure. The payload includes a water-solublepesticide and, optionally, additional components (e.g., water,additives, and/or other solvents).

The pesticide and other optional payload components in the mixture thenenter the open pores. This pesticide loading step is followed by a stepof closing the pores in the absence of actinic radiation. The mixturecontaining the pesticide-loaded uncapped particles 520 is exposed toelectromagnetic radiation at wavelengths greater than approximately 300nm (e.g., approximately 290 nm-800 nm). This allows the stilbenoidcompound 540 units in the photosensitive polymer to re-dimerize in theabsence of actinic radiation, once again capping the pores. Capping thepores yields porous sustained-release pesticide capsules 505. When theporous capsules 505 are exposed to radiation at wavelengths ofapproximately 240 nm or below, retro-dimerization will again occur,causing the pores to open, and the pesticide to be released. Radiationat these wavelengths can be provided by sunlight, or by artificiallighting.

The porous capsules 505 are optionally incorporated into a polymermatrix, combined with carrier fluids, and/or combined with additives.The capsules 505 are then deposited onto surfaces as pesticide coatings.The porous capsules 505 are not illustrated as having orthogonalfunctionalities. However, in some embodiments, the porous capsules 505have orthogonal functionalities that facilitate incorporation of thecapsules 505 into a polymer matrix by binding. Additives and/oradditional pesticides can also be bound to the orthogonalfunctionalities. Examples of polymer matrices, additional pesticides,carrier fluids, and additives that can be included in the pesticidecoatings along with the porous capsules 505 are discussed in greaterdetail above.

The processes discussed herein and their accompanying drawings are notto be construed as limiting. One skilled in the art would recognize thata variety of techniques may be used that vary in conditions, components,methods, etc., which ultimately generate sustained-release pesticidematerials and coatings. In addition, the conditions can optionally bechanged over the course of a process. Further, in some embodiments,processes can be added, omitted, or carried out in alternate orders,while still remaining within the scope of the disclosure, as will beunderstood by a person of ordinary skill in the art. It should also benoted that processes can be carried out by a single entity, or bymultiple entities. For example, a first entity may produce thepesticides, a second entity may produce the hydrogels or microcapsules,and a third entity may deposit the sustained-release pesticide materialson a surface.

What is claimed is:
 1. A sustained-release pesticide coating,comprising: a pesticide underlayer to be deposited on a surface; aphotodegradable hydrogel layer deposited on the pesticide underlayer,wherein the photodegradable hydrogel layer is formed by reacting 4-armedalkyne-terminated polyethylene glycol (PEG) monomers with 4-armedcoumarin azide-terminated PEG monomers, wherein: each terminalfunctional group on the 4-armed alkyne-terminated PEG monomers has theformula:

and each terminal functional group on the 4-armed coumarinazide-terminated PEG monomers has the formula:

and a pesticide overlayer deposited on the photodegradable hydrogellayer, wherein the photodegradable hydrogel layer temporarily preventscontact between the pesticide overlayer and the surface.
 2. Thesustained-release pesticide coating of claim 1, further comprising atleast one material selected from the group consisting of an additionalpesticide, a binder, a carrier fluid, and an additive.
 3. Thesustained-release pesticide coating of claim 2, wherein the additive isselected from the group consisting of a colorant, a corrosion inhibitor,a stabilizer, a hardener, a co-solvent, and a plasticizer.
 4. Thesustained release pesticide coating of claim 1, wherein the pesticideunderlayer comprises a first pesticide directed to a first type oforganism and a second pesticide directed to a second type of organism.5. The sustained release pesticide coating of claim 1, wherein thepesticide underlayer comprises a first pesticide directed to a firsttype of organism and the pesticide overlayer comprises a secondpesticide directed to a second type of organism.
 6. The sustainedrelease pesticide coating of claim 1, wherein the photodegradablehydrogel layer is formed in an azide-alkyne cycloaddition reaction. 7.The sustained release pesticide coating of claim 1, wherein thepesticide underlayer comprises at least one pesticide blended with apolymer adhesive binder.
 8. The sustained release pesticide coating ofclaim 1, wherein the pesticide underlayer comprises at least onepesticide blended with an adhesive additive.
 9. The sustained releasepesticide coating of claim 1, wherein the pesticide overlayer comprisesat least one pesticide blended with a polymer adhesive binder.
 10. Thesustained release pesticide coating of claim 1, wherein the 4-armedalkyne-terminated PEG monomers are formed in a process comprising:forming a solution of 4-armed polyethylene glycol amine-HCl and excesstriethylamine; and adding 4-pentynoic acid, diisopropyl carbodiimide,and diethyl aminopyridine to the solution.
 11. The sustained releasepesticide coating of claim 1, wherein the 4-armed coumarin-azide PEGmonomers are formed in a process comprising: forming a solution of4-armed polyethylene glycol tetra-carboxylic acid and excessN,N-diisopropyl ethylamine; forming a mixture of1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4, 5,-b]pyridinium3-oxid hexafluorophosphate and the solution; and adding a solution ofcoumarin azide and N,N-diisopropyl ethylamine to the mixture.
 12. Thesustained release pesticide coating of claim 10, wherein the 4-armedpolyethylene glycol amine-HCl has a molecular weight ranging fromapproximately 300 Da-20,000 Da.
 13. The sustained release pesticidecoating of claim 11, wherein the 4-armed polyethylene glycoltetra-carboxylic acid has a molecular weight ranging from approximately300 Da-20,000 Da.